The present invention relates to a device for automatically controlling and compensating the level of chemical treatment baths that has particular application to automatic machines for developing photographic film and/or exposed light-sensitive paper. More precisely, the present invention allows automatic compensation for the loss of water through evaporation from such baths. Conventionally, in automatic machines for developing exposed photographic film or printed light-sensitive paper, known as film developers and print developers, sets of baths containing aqueous solutions of suitable chemical products are required for the progressive implementation of various processing stages through which a film or paper to be treated will be gradually directed.
Likewise conventionally, the entire operation is carried out at a temperature of 40.degree. C., approximately, and the interior of a relative enclosure is continuously ventilated for the purpose of expelling such vapors as may be given off.
During such an operation, the passage of the film or paper through the treatment baths will occasion a gradual depletion of the solution. This is compensated by the addition of corresponding fresh chemical solutions, a step piloted automatically on the basis of the surface treated.
Beside depletion by consumption, with liquid being removed gradually as the treated film or paper is fed through, there is at the same time a certain loss due to evaporation of the water in the different solutions, occasioning a drop in the level of the various baths, which hitherto has been manually compensated by adding an appropriate quantity of water.
Whether processing is interrupted temporarily, with breaks occurring normally once per day and lasting for a full shutdown period, typically from the evening when operation is suspended through to the following morning, or more especially where breaks are of longer duration, such as at weekends or over holiday periods, when stoppages may even run into a number of days, the evaporation of water occasions a corresponding pronounced drop in the level of the baths, to a greater or lesser degree. This cannot be compensated simply by the addition of new solution, as this would result in a progressively higher concentration, tending to change the characteristics of treatment. Besides, further drawbacks may be brought on, namely, the formation of deposits due to crystallization on the components by which the film or paper is conveyed through the various treatment baths, and consequently a degradation of their ultimate characteristics.
Moreover, film or paper feed rollers not immersed in the relative baths are continuously moistened during operation by the solution carried onto their surfaces by the running film or paper. As a result of the drying which occurs during shutdown periods, prolonged or otherwise, deposits of the chemical substances from the solutions are left on the rollers. Normally, this does not cause difficulties in the case of the rollers by which film or paper is transferred from one bath to the next, since as the machine resumes operation these rollers are immediately moistened, and any deposits left on their surfaces will be redissolved and removed.
However, it is common, particularly in the case of film developers, for the machine to be equipped with devices positioned at the point of exit from the final bath and designed to effect a suitable uniform removal of the greater part of the solution still clinging to the opposite surfaces of the film, thereby avoiding the formation of haloes and/or stains during the successive drying stage, which besides spoiling the appearance of the film can also lead to problems with its subsequent reproduction. In a conventional solution, such devices consist of two pairs of rollers fashioned from a suitable porous and flexible material. The two rollers of each pair are disposed in mutual opposition and pressed one against the other in such a manner that the covering of liquid clinging to a film passing between them will be removed uniformly.
These rollers, commonly referred to as squeeze rollers, will themselves clearly be moistened during operation by the selfsame solution they are designed to remove, and thus remain impregnated. With the evaporation of water from the impregnating solution during periods when the operation is suspended, deposits are formed due to crystallization of the substances dissolved in the solution. The deposits are unable to redissolve quickly at the moment when operation is resumed, and thus the deposits in question can cause damage even of a notable and irreparable nature, particularly to the first film with which contact is made after resumption of operation.